| 摘要 |
PROBLEM TO BE SOLVED: To provide a method by which foreign matter existing on a surface of an inspection target object having a rugged sheet can be detected with high accuracy.SOLUTION: There is provided the method for detecting foreign matter existing on a surface of a sheet 100 in an inspection target object, the surface of the sheet 100 having a rugged shape. The method includes a step of irradiating an inspection target surface 100a of the sheet 100 with light, receiving reflected light R of the irradiation light and determining whether or not foreign matter exists on the inspection target surface 100a on the basis of the intensity of the reflected light R. An incident direction of the light with which the inspection target surface 100a is irradiated, is inclined at a predetermined angle with respect to the direction H orthogonal to the inspection target surface 100a. The inclined angle is made smaller than an angle &thetas; formed between the tangent drawn from the central point of one recessed portion 101 to a projected portion 102 located closest to the recessed portion and the direction H orthogonal to the inspection target surface 100a. |
